JP5798376B2 - Method for determining structural specifications of embedded piles - Google Patents

Description

  The present invention relates to a method for determining the structural specifications of an embedded pile, and more particularly to a method of determining the specifications of a pile body having a protrusion such as a node at the tip and a rooting portion into which the tip is inserted.

  There is an embedded pile construction method in which a soil-solidified part is formed at the bottom of the pile hole, and a prefabricated pile, such as a pre-made pile having a node at the lower end, is embedded in the pile hole so that the node enters the rooted part. Are known.

  In such an embedded pile construction method, in order to prevent the ready-made pile from subsidizing due to the load applied to it, the ground supporting force at the root consolidation part is greater than the design load, and the It is necessary to ensure unity.

  In order to make the pile body and the root consolidation part specification satisfying the above requirements, conventionally, a simple method of setting the root consolidation part diameter and the nodal part diameter and determining the required soil cement strength from the FEM analysis results. Has been taken.

  In the case of joint piles, if the integrity of the piles is secured, the support pressure acts on the joints, and if the pile tip is separated upward from the bottom of the piles, the separation height It has been found that the bearing pressure at the pile tip increases accordingly.

  However, since the conventional technique is made without taking these acting forces into consideration in determining the structural specifications, there is a problem that the strength of the soil cement becomes excessively high and is uneconomical.

  None

The present invention has been made based on the technical background as described above, and achieves the following object.
The object of the present invention is to consider that an advantageous bearing pressure is acting on the ready-made pile under the condition that the integrity of the ready-made pile and the root solidified part is ensured, and thereby the economical pile. It is providing the method which can be set as a body structure and a root structure part structure.

<Theoretical background of the present invention>
FIG. 1 shows a root cemented portion 2 made of soil cement formed at the bottom of a pile hole 4, and a node pile 1 embedded in the pile hole 4 so that a lower end portion having a node portion 3 enters the root consolidated portion 2. Is shown. Assuming that the integrity of the bottom end of the joint pile 1 arranged in the root consolidation part 2 and the root consolidation part 2 is secured, the joint pile 1 supports the load P and does not cause displacement in the vertical direction. The condition is that the supporting force acting on the root hardening part 2 from the ground is equal to or greater than the load P. The supporting force that opposes the load P is the sum of the tip supporting force Rp that acts on the bottom surface of the root consolidation portion 2 and the friction force Rf that acts on the peripheral surface of the root consolidation portion 2.
P ≦ Rp + Rf (1)
Indicated by

Here, as shown in FIG. 2, when paying attention to the joint pile 1, when the joint pile 1 receives the load P, a supporting pressure acts on the joint portion 3 and the tip of the pile as a force against this. Therefore, in order to satisfy the above assumption that the integrity of the tip portion and the rooted portion of the joint pile 1 is ensured and the joint pile 1 is not displaced in the vertical direction, the sum of these support pressures is the load. It is a condition that it is P or more. The condition is that R1 is the bearing pressure acting on each node 3, n is the number of nodes, and R2 is the pile tip bearing pressure.
P ≦ n · R1 + R2 (2)
Indicated by

  The parameters that determine the nodal support pressure R1 are the nodal diameter, shaft diameter, root consolidation strength determined by the root material (eg, soil cement), and the parameters that determine the overall support pressure are The number of nodes is n. The parameters that determine the pile tip support pressure R2 are the shaft diameter, the separation height of the pile tip from the bottom surface of the root consolidation portion 2 (the significance of which will be described later), and the like. Therefore, it is possible to select the optimum structural specifications of the pile body and the root-solidifying portion by changing each of the above parameters under the condition that the expressions (1) and (2) are satisfied.

The present invention has been made on the basis of the above knowledge, and employs the following means.
That is, the present invention is to Kuiana roots hardened portions by soil cement is formed in the bottom, the buried piles the knuckles prefabricated pile having knuckles on the lower end is buried so as to enter the root hardened portion The structural specification determination method of the following formulas (1) (2),
P ≦ Rp + Rf (1)
P ≦ n · R1 + R2 (2)
Where P: design load, Rp: tip support force acting on the bottom of the root consolidation part, Rf: frictional force acting on the periphery of the root consolidation part , n: number of nodes, R1: support acting on one node pressure, R2: to satisfy the pile tip Bearing force <br/>, to determine the specifications of the pile body and root consolidated unit, the following equation for the knuckles one Bearing force R1 (3)
R1 = α · qu × At (3)
However, alpha: bearing capacity coefficient (α = 1.0 ~2.0), qu : soil cement strength, At: knurl supporting pressure area
It is in the structural specification determination method of the embedded pile characterized by calculating from .

More specifically, to satisfy the above formula (2), set apart height from the root firm bottom face of the pile body, knurl diameter and Kuijiku portion diameter, the number and soil cement strength knuckles It is characterized by that.

  According to the present invention, under the condition that the integrity of the ready-made pile and the root solidified portion is ensured, the pile structure and the root are considered in consideration of the advantageous support pressure acting on the ready-made pile. Since the solidified portion structure is determined, the strength of the solidified portion and the like can be set to be sufficient to support the load, and an economical design can be achieved.

It is a figure which shows the force which acts on a root consolidation part when a pile body and a root consolidation part are united. It is a figure which shows the support pressure which acts on a pile body. It is a figure which shows the item of a pile body. It is a flowchart which shows the procedure of the determination method of a pile body and a solidified part structure specification. It is a flowchart following FIG. It is a graph which shows the relationship between soil cement strength and bearing strength. It is a graph which shows the relationship between pile tip separation height and the gain coefficient of the bearing pressure by it.

  FIG. 3 shows the specifications of the pile body and the root-solidified portion determined based on the present invention. De is the root consolidation part diameter, H is the root consolidation part height, H1 is the height of the pile tip from the bottom of the root consolidation part, Dn is the node part diameter, and Dp is the shaft part diameter. Hereinafter, the procedure for determining the structural specifications of the pile body and the rooting portion will be described with reference to the flowcharts shown in FIGS. 4 and 5.

1. Determination of design load P (step S1)
The design load P is a load (KN) supported by one node pile in the root consolidation part.
2. Determination of construction method (step S2)
The embedded pile construction method includes a ready-made pile construction method, a pre-boring construction method, and a medium digging construction method, and one of them is selected.

3. Calculation of ground bearing strength qd (step S3)
The bearing strength qd (see FIGS. 1 and 2) is a bearing strength that the tip ground of the root consolidation part 2 takes on and is calculated from the N value of the ground and the soil quality. For example, in the pre-boring method, the road bridge specifications specify sand ground: qd = 150N (≦ 7500kN / m ² ) and gravel ground: qd = 200N (≦ 10000kN / m ² ).
4). Setting of height of root consolidation part H and pile tip separation height H1 (step S4)
For example, the initial settings are H = 2.0 m and H1 = 0 m.

5. Calculation of root diameter De (Step S5)
The root diameter De is calculated from the above equation (1). In formula (1), the peripheral frictional force Rf is indicated by Rf = f · U · H (f: Friction force of the peripheral surface, U: Perimeter of root consolidation, H: Height of root consolidation) It is. The skin friction of f is a degree of frictional force responsible circumferential surface of the root hardened portion 2, if the pre-boring method is, for example, specifications for highway bridges, sand soil: f = 5N (≦ 150kN / m 2), Clay : F = 10 N (≦ 100 kN / m ² ) However, the peripheral friction force Rf is extremely smaller than the tip support force Rp and is zero as viewed from the safe side. Accordingly, the root diameter De is calculated by the following equation.
P = Rp + Rf
= Rp +0
= Qd · De ² · π / 4

6). Setting of node diameter Dn and shaft diameter Dp (step S6)
The node diameter Dn is set such that De> Dn + 50 with a margin of 50 mm, for example, with respect to the root diameter De in order to insert the pile into the root consolidation part. Normally, ready-made piles are standardized, and therefore, when a standard product with a value having a node diameter Dn is selected, the shaft diameter Dp is also determined by itself.
7). Calculation of joint bearing area At (Step S7)
The nodal bearing bearing area At is an area of the nodal portion protruding from the shaft portion. Since the node diameter Dn and the shaft diameter Dp are set, the node bearing area At is calculated by the following equation.
At = (Dn ² −Dp ² ) · π / 4

8). Setting of soil cement strength qu (Step S8)
As the soil cement strength qu, an appropriate value is selected within the range of 5 to 30 N / mm ² . However, if the pile tip separation height H1> 0, the ground support strength qd ≦ soil cement strength qu.
9. Calculation of bearing strength from soil cement strength qu (Step S9)
The bearing strength here refers to the strength of the soil cement when the load is supported only by the joints. The inventors of the present invention have made a device in which the bearing pressure does not act on the tip of the pile within the rooting portion, but the bearing pressure acts only on the node, and the pile is supported by applying a load to the pile. Was measured, and it was found that there was a relationship as shown in FIG. 6 between the soil cement strength qu and the bearing strength. That is, the bearing strength is α · qu (α: bearing strength coefficient, α = 1.0 to 2.0), and the bearing strength can be greater than the soil cement strength qu. Therefore, α is appropriately selected from the range of 1.0 to 2.0 to calculate the bearing strength.

10. Calculation of bearing pressure R1 for one joint (step S10)
The bearing pressure R1 of one node can be obtained from the formula of bearing pressure R1 = bearing strength × bearing area At using the bearing area At calculated in step S7 and the bearing strength calculated in step S9. .
11. Set the number of nodes (Step S11)
The initial setting is, for example, n = 2.

12 Calculation of joint support pressure and pile tip support pressure (Step S12)
The nodal support pressure is the sum of the support pressures acting on the individual nodal parts, and can be obtained by multiplying the nodal support pressure R1 calculated in step S10 by n. On the other hand, with regard to the pile tip support pressure R2, according to the experiments of the inventors of the present invention, when the pile tip is separated upward from the bottom of the rooting portion, the support pressure increases in proportion to a certain height. It has been found. In FIG. 7, the ratio of the shaft diameter Dp to the separation height H1 is taken on the horizontal axis, and the gain factor β (≧ 1) is obtained by adding 1 to the ratio of the increase in the support pressure obtained by the separation, It is a graph taken on the axis.

The pile tip support pressure R2 is calculated from R2 = (Dp ² · π / 4) · qd · β by using the shaft diameter Dp, the bearing capacity qd of the ground and the gain coefficient β due to the separation shown in the graph. Here, when the separation height H1 = 0, that is, β = 1 when the pile tip is inserted to the bottom of the rooting portion, and when H1> 0, that is, when the pile tip is separated from the bottom of the rooting portion, β > 1.
13. Judgment of integrity of pile body and root-solidified part (step S13)
As described above, when the nodal support pressure nR1 and the pile tip support pressure R2 are calculated, it is determined whether or not the above formula (2) is satisfied. If the formula (2) is satisfied, the integrity of the pile body and the root solidified part is ensured. Therefore, the parameters related to the calculation of the nodal support pressure nR1 and the pile tip support pressure R2 should be set values. Determine the structure of the piles and roots.

  On the other hand, if the nodal support pressure nR1 and the pile tip support pressure R2 do not satisfy the formula (2), step S4 and subsequent steps are executed again, and each parameter involved in the calculation of the nodal support pressure nR1 and the pile tip support pressure R2 is calculated. Reset the value of. The parameter for changing the setting value is at least one of the pile tip separation height H1, the node diameter Dn, the shaft diameter Dp, the soil cement strength qu, and the number n of the nodes. Good.

  As a pile body structure to which the present invention can be applied, when a node portion is provided as a projection portion, at least one is sufficient. The protruding portion is not limited to the node portion, and a plurality of protruding portions may be provided on the peripheral surface of the shaft portion so as to be annular at intervals. The pile body may be a concrete pile or a steel pipe pile. As a root-solidification part structure, the expansion root-consolidation part formed by expanding the lower part of a pile hole, or the root-consolidation part which does not expand may be sufficient. The root hardening material is generally a soil cement formed by mixing and stirring excavated soil and cement milk, but may be another solidifying material such as cement mortar alone.

1: Ready-made pile (node pile)
2: Rooting part 3: Node part

Claims (2)

In the method of determining the structural specifications of an embedded pile in which a pile is formed with a soil cement root at the bottom and a pre-made pile having a node at the lower end is embedded so that the node enters the root consolidation And the following formulas (1), (2),
P ≦ Rp + Rf (1)
P ≦ n · R1 + R2 (2)
Where P: design load, Rp: tip support force acting on the bottom of the root consolidation part, Rf: frictional force acting on the periphery of the root consolidation part , n: number of nodes, R1: support acting on one node pressure, R2: to satisfy the pile tip Bearing force <br/>, to determine the specifications of the pile body and root consolidated unit, the following equation for the knuckles one Bearing force R1 (3)
R1 = α · qu × At (3)
However, alpha: bearing capacity coefficient (α = 1.0 ~2.0), qu : soil cement strength, At: knurl supporting pressure area
A structural specification determination method for embedded piles, characterized in that So as to satisfy the above formula (2), claims and setting apart from the root firm bottom face of the pile body height, knurl diameter and Kuijiku portion diameter, the number and soil cement strength knuckles Item 3. A method for determining the structural specifications of an embedded pile according to item 1.

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